---
title: Caching
hide_title: true
sidebar_position: 6
version: 1
---

## Caching

Superset uses [Flask-Caching](https://flask-caching.readthedocs.io/) for caching purposes.
Flask-Caching supports various caching backends, including Redis (recommended), Memcached,
SimpleCache (in-memory), or the local filesystem.
[Custom cache backends](https://flask-caching.readthedocs.io/en/latest/#custom-cache-backends)
are also supported.

Caching can be configured by providing a dictionaries in
`superset_config.py` that comply with[the Flask-Caching config specifications](https://flask-caching.readthedocs.io/en/latest/#configuring-flask-caching).

The following cache configurations can be customized in this way:
- Dashboard filter state (required): `FILTER_STATE_CACHE_CONFIG`.
- Explore chart form data (required): `EXPLORE_FORM_DATA_CACHE_CONFIG`
- Metadata cache (optional): `CACHE_CONFIG`
- Charting data queried from datasets (optional): `DATA_CACHE_CONFIG`

For example, to configure the filter state cache using redis:

```python
FILTER_STATE_CACHE_CONFIG = {
    'CACHE_TYPE': 'RedisCache',
    'CACHE_DEFAULT_TIMEOUT': 86400,
    'CACHE_KEY_PREFIX': 'superset_filter_cache',
    'CACHE_REDIS_URL': 'redis://localhost:6379/0'
}
```

### Dependencies

In order to use dedicated cache stores, additional python libraries must be installed

- For Redis: we recommend the [redis](https://pypi.python.org/pypi/redis) Python package
- Memcached: we recommend using [pylibmc](https://pypi.org/project/pylibmc/) client library as
  `python-memcached` does not handle storing binary data correctly.

These libraries can be installed using pip.

### Fallback Metastore Cache

Note, that some form of Filter State and Explore caching are required. If either of these caches
are undefined, Superset falls back to using a built-in cache that stores data in the metadata
database. While it is recommended to use a dedicated cache, the built-in cache can also be used
to cache other data.

For example, to use the built-in cache to store chart data, use the following config:

```python
DATA_CACHE_CONFIG = {
    "CACHE_TYPE": "SupersetMetastoreCache",
    "CACHE_KEY_PREFIX": "superset_results",  # make sure this string is unique to avoid collisions
    "CACHE_DEFAULT_TIMEOUT": 86400,  # 60 seconds * 60 minutes * 24 hours
}
```

### Chart Cache Timeout

The cache timeout for charts may be overridden by the settings for an individual chart, dataset, or
database. Each of these configurations will be checked in order before falling back to the default
value defined in `DATA_CACHE_CONFIG.

Note, that by setting the cache timeout to `-1`, caching for charting data can be disabled, either
per chart, dataset or database, or by default if set in `DATA_CACHE_CONFIG`.

### SQL Lab Query Results

Caching for SQL Lab query results is used when async queries are enabled and is configured using
`RESULTS_BACKEND`.

Note that this configuration does not use a flask-caching dictionary for its configuration, but
instead requires a cachelib object.

See [Async Queries via Celery](/docs/installation/async-queries-celery) for details.

### Caching Thumbnails

This is an optional feature that can be turned on by activating it’s [feature flag](https://superset.apache.org/docs/installation/configuring-superset#feature-flags) on config:

```
FEATURE_FLAGS = {
    "THUMBNAILS": True,
    "THUMBNAILS_SQLA_LISTENERS": True,
}
```

By default thumbnails are rendered per user, and will fall back to the Selenium user for anonymous users.
To always render thumbnails as a fixed user (`admin` in this example), use the following configuration:

```python
from superset.tasks.types import ExecutorType

THUMBNAIL_SELENIUM_USER = "admin"
THUMBNAIL_EXECUTE_AS = [ExecutorType.SELENIUM]
```


For this feature you will need a cache system and celery workers. All thumbnails are stored on cache
and are processed asynchronously by the workers.

An example config where images are stored on S3 could be:

```python
from flask import Flask
from s3cache.s3cache import S3Cache

...

class CeleryConfig(object):
    broker_url = "redis://localhost:6379/0"
    imports = ("superset.sql_lab", "superset.tasks", "superset.tasks.thumbnails")
    result_backend = "redis://localhost:6379/0"
    worker_prefetch_multiplier = 10
    task_acks_late = True


CELERY_CONFIG = CeleryConfig

def init_thumbnail_cache(app: Flask) -> S3Cache:
    return S3Cache("bucket_name", 'thumbs_cache/')


THUMBNAIL_CACHE_CONFIG = init_thumbnail_cache
# Async selenium thumbnail task will use the following user
THUMBNAIL_SELENIUM_USER = "Admin"
```

Using the above example cache keys for dashboards will be `superset_thumb__dashboard__{ID}`. You can
override the base URL for selenium using:

```
WEBDRIVER_BASEURL = "https://superset.company.com"
```

Additional selenium web drive configuration can be set using `WEBDRIVER_CONFIGURATION`. You can
implement a custom function to authenticate selenium. The default function uses the `flask-login`
session cookie. Here's an example of a custom function signature:

```python
def auth_driver(driver: WebDriver, user: "User") -> WebDriver:
    pass
```

Then on configuration:

```
WEBDRIVER_AUTH_FUNC = auth_driver
```
